AIRCRAFT DESIGN LECTURE 4 : AIRCRAFT PROPULSION

Transcription

1 AIRCRAFT DESIGN LECTURE 4 : AIRCRAFT PROPULSION 09/29/2017 Remy Princivalle Remy.princivalle@techspace-aero.be +32 (0)

2 Agenda 0. INTRODUCTION & HISTORY 1. PROPULSION 2. ENERGY GENERATION 3. ENERGY SOURCE 4. PROPULSION SYSTEM 2

3 INTRODUCTION A bit of history

4 What is propulsion? Propulsion system provides the needed translation force from a dedicated power source > Several energy available (combustible -oil, gas, wood-, electrical, chemical, animal ) > Several way to consume energy into power (muscle, piston, turbine ) > Several way to generate the translation force (propeller, nozzle, wing ) At the end of this lecture, you should know > The several types of existing propulsion systems (or how to invent a new one?) > How to choose one or one other > The key parameters to define the right dimensions of your propulsion system 4

5 A bit of history : at the beginning was Before humans > Birds and insects propulsion is included into their wings motion. Energy : nutrition Power : muscle Force : wing motion Human tried to copy them > Thank you Leonard, but it was not really efficient 5

6 Getting around propulsion difficulties During 18 th, Montgolfier brothers got an easier idea to fly > Energy is used to heat the air inside the balloon But no real way of propulsion included Finally, requires a lot of energy to fly But no energy dedicated to movement Energy : hope Power : none Force : wind 6

7 Then propulsion appeared Mid 19 th, first dirigibles appeared > Henri Giffard used steamed powered propeller And propeller and planes were associated late 18 th / early 19 th > Clément Ader and the Avion III > The Wright brothers and the Flyer Energy : combustible Power : piston Force : propeller Finally, human lately found the way to associate propulsion and wing movement > First helicopter in early 20 th Energy : combustible Power : piston Force : rotating wing 7

8 Propulsion evolution 1. the piston engine Steam engine early 1900 Associated with propeller V engines WW1 & 2 Star fixed & rotating engines WW1 & 2 Challenge was - Increasing power density - lowering vibrations due to engine Wankel engines >

9 How does different piston engine types work? In-line pistons => Virabtions Star pistons but no smoothed vibrations No axial piston : totally smoothed But what about leakages? V pistons => 1st step smoothing Star pistons : mostly smoosthed try to imagine the center fixed and pistons turning with propeller 9

10 Propulsion evolution 2. the gas turbine engine Turbojet Associated with propeller, fan or single nozzle Afterburn jet engine Turbofan High power density Turboprop Challenge was - High speed, high temperature materials - Component efficiency 10

11 How do different piston engine types work? the gas generator : - Compress air for efficient combustion - Burn fuel to energize the gas - Get the necessary work for compressor inside HPT If efficient components => residual pressure at outlet to be used Or into a gearbox & helicopter rotor Into a single nozzle for high thrust with low air flow - even more when after burning - Into a fan for a chosen compromise between size and fuel consumption Into a gearbox & propeller for high propulsion efficiency 11

12 The last present and the future for planes : the electric engine e-fan Elektra prop Solar impulse fierfly Energy : electricity Power : electric engine Force : prop or fan 12

13 The forgotten past : the nuclear airplane Energy : atomic Power : nuclear engine Force : nozzle 13

14 And don t forget space & rockets! Solid propulsion Associated with nozzles Liquid propulsion Cryogenic propulsion Plasma propulsion (satellites) Needs high thrust to weight ratio for vertical acceleration 14

15 1 THE PROPULSION MEDIA 15

16 The main way of propulsion The open rotor > Very efficient > High cruise speed > Big size > Very noisy > Complexity The nozzle > Small size & weight > Simplicity > The highest speeds > Poor efficiency The propeller > The best efficiency > Big size > Limited cruise speed The fan > Good efficiency > High cruise speed > Mid size > Low noise > Shroud additionnal weight 16

17 The PROPELLER : the basics Propeller traction is generated thanks to its aero profile lifting > As a wing, but its movement is perpendicular to the plane thanks to rotation speed > => lift is moving forward instead of moving up lift traction Plane speed WING Rotation speed PROPELLER The propeller traction depends on (Habott law) > Its rotation speed > Its diameter > Its staggering > And proportionnal to air density 17

18 The PROPELLER : more details Propeller traction and power consumption can be read on its characteristics > Function of J = V/n.D > Ct = traction coefficient > Cp = power coefficient > eta = propeller efficiency Traction calculation : > Power calculation > Efficiency > eta = T.V / P = Ct/n.D.Cp. V > eta = J.Ct/Cp 18

19 The NOZZLE THRUST equation is : > Thrust = q. (Vejection Vinlet) q = air mass flow As Ps = Pt rho V² You can do thrust thanks to > Pressure Air intake recovery pressure (RAM jets) Gas generator Compressor Mainly a fan (see later) > High speed Convergent or Convergent/divergent section Pressure and speed are closely linked Rockets combustion Gas generator post combustion > High flow (increase A & Q), meaning size of the nozzle 19

20 The NOZZLE : more details Ejection speed Ve : > Outlet ambiant pressure P0 > Nozzle inlet total pressure Pt > Ejection pressure losses DP => Pt DP = Ps + ½ ρ. Ve² Propulsion efficiency > Effective propopulsion power : T. V0 = q. V0. (Ve V0) > Power given to the air : ½ q ( Ve² - V0²) Propulsive efficiency : > Etaprop = 2.V0. (Ve V0) / (Ve² - V0²) = 2 / (1 + Ve/V0) 20

21 The FAN : the basics It s like a propeller, but with a shroud and a nozzle > The fan sucks air and brings speed and pressure to it > This pressure is canalized through the shroud and the nozzle > And then ejected with speed that generates the thrust 21

22 The FAN : more details Fan noozle air ejection speed : > Ambient pressure = Ps0 > Fan inlet total pressure : > Fan pressure ratio : > Nozzle ejection : > As PsE = PS0 at ejection, but TsE > Ts0, > RhoE = Ps0 / Rgaz.TsE Ptin = Ps0 + ½ rho0 V0² Ptout = FPR. (Ps0 + ½ rho0 V0²) Ve² = 2.Ps0/rhoE.(FPR-1) + rho0/rhoe FPR V0² Ve² = TsE.( 2.Rgaz.(FPR-1) + 1/Ts0. FPR V0²) Fan pressure ratio Cruise speed 22

23 2 THE POWER GENERATOR 23

24 DIFFERENT WAYS TO GENERATE THE POWER Pedals Piston engine Gas generator Turbine Fuel Cell Electrical engine Combustion 24

25 DIFFERENT WAYS TO GENERATE THE POWER Pedals Piston engine Gas generator Electrical engine Propeller Combustion Turbine Fuel Cell 25

26 DIFFERENT WAYS TO GENERATE THE POWER Pedals Piston engine Gas generator Electrical engine Propeller Combustion Turbine Fuel Cell 26

27 DIFFERENT WAYS TO GENERATE THE POWER Pedals Piston engine Gas generator Electrical engine Propeller Combustion Turbine Fuel Cell 27

28 DIFFERENT WAYS TO GENERATE THE POWER Pedals Piston engine Gas generator Electrical engine Propeller Combustion Turbine Fuel Cell 28

29 DIFFERENT WAYS TO GENERATE THE POWER Pedals Piston engine Gas generator Turbine Fuel Cell Electrical engine Combustion Propeller 29

30 DIFFERENT WAYS TO GENERATE THE POWER Pedals Piston engine Gas generator Fan + Nozzle Turbine Fuel Cell Electrical engine Combustion 30

31 DIFFERENT WAYS TO GENERATE THE POWER Pedals Piston engine Gas generator Fan + Nozzle Turbine Fuel Cell Electrical engine Combustion 31

32 DIFFERENT WAYS TO GENERATE THE POWER Pedals Piston engine Gas generator Combustion Turbine Fan + Nozzle Fuel Cell Electrical engine 32

33 DIFFERENT WAYS TO GENERATE THE POWER Pedals Piston engine Gas generator Single Nozzle Turbine Fuel Cell Electrical engine Combustion 33

34 DIFFERENT WAYS TO GENERATE THE POWER Pedals Piston engine Gas generator Single Nozzle Turbine Fuel Cell Electrical engine Combustion > Gaz > Pouder > liquid 34

35 DIFFERENT WAYS TO GENERATE THE POWER Pedals Piston engine Gas generator Turbine Fuel Cell Electrical engine Combustion 35

36 PEDALS Strong cycle champion is around 300W average, 500W peak > Even Lance Armstrong is less than peak power kw/kg Poor efficiency 36

37 ELECTRICAL ENGINE Widely used from 1W to 100kW 2kW/kg 90% efficiency > But have a look at the Tesla engine (~500kW) > Or the Airbus light aircraft demonstrator More and more powerfull in the future for a lighter weight 37

38 ELECTRICAL ENGINE FUNCTIONNING Functionning : > Magnet rotor induced in rotation through changing phase stators 38

39 PISTON ENGINE Widely used from 5kW (mower) to 500kW 0.5kW/kg ~50% efficiency > Can easily rise up to 800kW and even more but with heavy mass cost > Can be turbocharged for higher power density & efficiency Enables constant power with altitude thanks to adapted compression level 39

40 PISTON ENGINE FUNCTIONNING Piston engine thermodynamic cycle Combustion is close to stoechiometric > ~14 fuel/air ratio Air mass flow proportionnal > to rotation speed divided by 2 (4 steps engines) > to athmosphere density, as constant volume => engine power proportionnal to speed untill mechanical losses increase at very high speed => engine power mainly proportionnal to air density > But some constant losses lead to the following approximated equation PW ~ PW0. (1.132 rho/rho ) PW0 = power at sea level Rho0 = air density at sea leve: 40

41 TURBO- (or SUPER-) CHARGED piston engine Increase of piston air inlet density by a comressor > Increase the piston engine power > Increase the diesel themodynamic cycle efficiency But needs power to drive the compressor > Directly driven on the engine power shaft => supercharger Compressor speed proportionnal to engine rotation speed End shaft power lower than piston power > Driven by an independent electric engine => e-charger Help-yourself compressor speed > Driven by an independent turbine on the exhaust gaz Compressor speed unlinked from engine speed, but not a la carte Turbine power extraced from piston power when exhausting (1->I cycle step) 41

42 THE GAS GENERATOR The gas generator in 3 parts engine (Brayton cycle) : > One compressor that increases thermal efficiency > One constant pressure combustion chamber By opposition to constant volume combustion of a piston > One turbine that take a part of the exhaust gas energy to drive the compressor 10kW/kg 40% to 50% efficiency The gas generator is associated > To a turbine that drives power to propeller or fan Can be a free low pressure turbine Or the same turbine than the compressor one, with extra-power going to the power shaft > To a nozzle for straight propulsion 42

43 GAS GENERATOR ADVANTAGES The higher pressure combustion enables higher extra-power at turbine outlet This is constant continuous air admission > By opposition to piston, that is 1 step admission per round > => High power density / small size GAS GENERATOR DISADVANTAGES Combustion temperature limited by turbine materials capability > 3% to 7% (cooled turbines) fuel/air ratio, ie half to quarter of piston engine Starting and Idle is touchy High rotation speeds needed > Cutting edge technologies > Meaning Gearbox necessary foe law speeds to propeller for example High altitude impact > Power propotionnal to inlet pressure and squared temperature 43

44 GAS GENERATOR AND ALTITUDE Gas generator power and fuel consumption is function of pressure and temperature : > We introduce the reduced power = PW= > And the reduced fuel flow = = Then fuel consumption is an easy equation from power : > WFR = A. PWR + B To determine A & B > Specific fuel consumption (SFC = WF / PW) at peak efficient point 0.2 kg/kw.h (big generators) to 0.3 kg/kw.h (small generators) > Idle (i.e. zero power) fuel consumption ~10% of full power consumption The energy required to make the compressor running to feed the fuel combustion 44

45 3 THE SOURCE OF ENERGIE 45

46 DIFFERENT SOURCES OF ENERGY Electricity Petroleums Solar energy Hydrogene Uranium >Not in Earth sky, please! 46

47 DIFFERENT SOURCES OF ENERGY Electricity > ULM > Short range > Low payload > Prototypes > Drones 47

48 DIFFERENT SOURCES OF ENERGY Electricity > But heavy batteries > Wide surface > Very low payload > Night concern Solar energy Uranium > Not on Earth sky, please 48

49 DIFFERENT SOURCES OF ENERGY Hydrogen Future could be solid hydrogen storage > High density > High pressure storage > Dangerous 49

50 DIFFERENT SOURCES OF ENERGY Petroleums > Easy & light storage > Easy use > Kerosene (JET-A1) : does not freeze > Gasoil : buy it anywhere 50

51 MATERIALS HEATING VALUE Combustible MJ/kg kj/l kj/mol Propane 50, Gasoil 44, Éthanol 29, Essence 47, Dihydrogène 120,5 12,75 (gaz) 286 Charbon Bois Battery (elec)

52 4 PROPULSION SYSTEM PRE-DESIGN 52

53 The type of propulsion system How to choose between propeller, turbofan, turbojet or even ramjet? > From your cruise speed! > 0.1 < Mn < 0.7 => propeller > 0.7 < Mn < 1.0 => turbofan The higher cruise speed, the lower bypass ratio > Mn > 1.0 => turbojet > Mn > 2 = RAMjet or SCRAMjet > RAMjet uses aircraft speed recovery for compression P = Ps0 + ½ rho V² needs to be associated with jet engine for reaching the right speed > SCRAMjet is RAMjet with still supersonic combustion 53

54 The number of engines Small aircraft often have a single engine > From general aviation to small bizprop as TBM700 Having at least second engine is much more secure for commercial aviation Transoceanic aircraft with 3 to 4 engines got advantageous, untill last twin 180min twin engines ETOPS aircraft > From A340 to B777 54

55 Engine installation Turboprops are mainly installed > On the noze for single engines > Under the wings for twin or 4 engines 55

56 Engine installation Turbofan can be installed > Under the wings > On the rear side of the fuselage > In the tail > In the wing > And some research with engines on top of the fuselage (especially delta planes) or the tail (Airbus) Easier for very high by-pass ratios 56

57 Engine installation Turbojets, the most often on military aircrafts > Mainly install inside the aircraft backside 57

58 Engine installation Engine installation induces loss of engine power > Because of pressure drops in air intakes and exhausts Noze, tails and in the aircraft installations especially Can reach 10% of engine power > Because of aereodynamics perturbations Propeller / wings interactions (lead to contrarotatives propellers on A400M for example) Distorsion due to incidence of engine vs. aircraft speed vector, proximity of fuselage Ground effect > Due to power and air off-take from the engine to the aircraft High pressure bleeds for cabin pressurization, anti-ice systems Mechanical off-take to an eletrical generator for aircraft power More than 10% of aircraft power on modern commercial aircrafts It can be estimated that the need of engine power is ~20% higher than what is needed for the propulsion 58

59 The Propeller Sea level traction of the propeller is defined by the aircraft cruise speed and altitude Size and number of propellers is chosen to get the right traction with the right diameter > You can deduce diameter (D) and rotation speed (N) thanks to Habott law and some existing propellers T = x pas x D 3 x N² x > And the J factor J = N.V/D Thanks to Cp, Ct and cruise speed, get the needed power > Consider some installation losses for the engine > => the power generator size to choose is now known How to choose between the different generator? > Big powers leads to gas generator (>1MW) > Small power leads to piston or electric engine (<100kW) > 0.1 to 1MW offers the choice 59 > Think at the engine weight + energy weight to choose your engine From heating value and thermal efficiency you get the weight of needed source of energy Don t forget the tank weight, that can be really heavy for electrical battery or liquid hydrogen for example! > And at the type of payload you target If only 2 people inside, you can imagine some eccentricities like solar impulse If 600 people inside, the lighter engine + fuel, the better

60 Piston vs. gas generator Piston engine is more fuel efficient for small size engines, but much heavier > Because of constant volume combustion efficiency (piston) that is better than constant pressure combustion (gaz generator) > Small airplanes like to use piston engines > Where small helicopters like better gas turbines For large turbofans, fuel efficiency reaches piston engine levels > Because high scale enables very high pressure ratio (>40) et high by-pass ratios (>5) on turbofans 60

61 The turbofan The size of the turbofan will depend of its by-pass ratio > The highest by-pass ratio, the lower fuel consumption > Why? : because thrust is done thanks to air flow instead of air ejection speed Etaprop = 2 / (1 + Ve/V0) > But the highest by-pass ratio, the highest fan diameter => weight, cost and drag increase The turbofan will run with a gas generator To determine the gas generator power : > From the required cruise thrust and speed, take-off thrust can be approximated as follow > = 1.!.! $ $ (.)/1.225."! # # G=0.9 for low bypass ratio, 1.2 for high bypass ratio Add installation thrust factor > Choose the by-pass ratio and determine the propulsion efficiency > For example : > CFM56-7B is ~90kN & q air ~300kg/s (61 ) => Ve-V0 = 300m/s (Ve/V0 = M0.8) Etaprop = 0.65 > Last very high BPR is same thrust but q air ~500kg/s (70 ) => Ve-V0 = 150m/s (Ve/V0 = M0.8) Etaprop = 0.75 > Gas generator power needed is PW = T. V0 / Etaprop / Eta_fan + non propulsive power 61

62 The turbojet The turbojet is needed for supersonic flights > Because drag (ie. Engine section) is more important than propulsion efficiency at high speed > Because light engine is more competitive for short time & quick climb missions The turbo jet is : > A gas generator (with 1 or 2 shafts) > A single nozzle > For the supersonic speeds, an afterburning increase ejection temperature => more thrust with equivalent pressure A small BPR ( ) is needed to feed afterburning with oxygen > Las turbojets have some higher BPR (0.4 for EJ200, 0.75 for F135) F135 is equivalent thrust as CFM56-5 in cruise with no after burning > But inlet diameter is 46 vs. 68 F135 is twice thrust than CFM56-7B in max thrust with after burning > 46 diameter could lift the B737 > When two 61 turbofan does 62

63 Between turbofan and turbojet For medium to long range fuel saving but with non-recurring and short time power increase > Shorter Climb > Non-recurring and/or short time supersonic Can be mixer turbojet and turbofan > Low BPR (~1-2?) to limit diameter, but reduce SFC > Possibility of after-burning in the nozzle for instantaneous power increase Let s have a look to such a pre-design > A good training as much of the components are involved : fan Nozzle Power generator After burning Let s specify the following engine : > A fan that feeds core inlet and secondary nozzle > A core, followed by afterburner and primary nozzle > Cruise at M0.8, and max speed at M1.2 > Alternative : Fan and core flows can be mixed before a common nozzle > A lot of others 63

64 Low BPR turbofan/jet pre-design 1. Which sort of power generator? > Piston engine will be too much inertia to accelerate supersonic in a short time > Piston engine will save fuel consumption, but its big size, then wider surface, will significantly impact the aircraft drag & mass, implying more engine power In fine as much fuel burn as gas generator as FB = SFC x PW > Electrical engine, with batteries, in such a hot environment as afterburning jet engine shall not be the best reliability option > The most intuitive choice is the gas generator Small sizing Low mass & inertia for good acceleration 2. Fan thermodynamics > Assume Mach 0.8 flight at sea level > Assume some quite high fan pressure ratio at 2.0 Station Pt (Pa) Tt (K) Ambiant Pamb/Tamb bar, 27 C Fan inlet P1/T Pt=Pamb + 1/2 rho V², Tt/Tamb=(Pt/Pamb)^((gamma-1)/gamma) Fan outlet P2/T FPR=2, if adiabatic : T2ad/T1=FPR^(0.4/1.4), as efficiency 0.9 :(T2-T1) = (T2ad-T1)/0.9 Nozzle Ve (m/s) = 571 Ve = sqrt((p2-pamb)/0.5rho), to determine rho : Ps=Pamb, Ts/T2=(Pamb/P2)^(0.4/1.4) > P2/T2 are also gas generator inlet conditions 64

65 Low BPR turbofan/jet pre-design 3. Gas generator thermodynamics > Gas generator first part is compressor > Assuming ~25 OPR (overall pressure ration = Pcombustion/P1) GG compressor shall have a 9 pressure ratio > Choose the inlet turbine temperature 1450K enables uncooled turbine rotor Cooled one could reach 1700K to 1900K Station Pt (Pa) Tt (K) GG inlet P2/T Combustion inlet P3/T efficiency :(T2-T1) = (T2ad-T1)/0.85 Combustion outlet P4/T T4 = 1450K for uncooled turbine (1700 to 1850K for cooled turbines) ; 2% pressure drop HP Turbine outlet T5/P efficiency :(T4-T5) = (T3-T2)/0.9 ; T5ad = T4-0.9*(T4-T5) = T4-T3+T2 > Fuel/Air ratio : FAR = [ Cp_air x (T4-T3) ] / FHV ~ 2% << 14% => there is still enough oxygen for afterburning 4. Fan turbine & primary nozzle > Here we have to choose BPR to determine the fan turbine power. T5-T6 = (BPR+1) x (T2-T1) / turbine_efficiency > I will assume a 1 BPR HP Turbine outlet T5/P efficiency :(T4-T5) = (T3-T2)/0.9 ; T5ad = T4-0.9*(T4-T5) = T4-T3+T2 LP turbine outlet T6/P efficiency :(T5-T6) = (T2-T1).(1+1)/0.9 Cold nozzle Ve (m/s) = 1119 Ve = sqrt((p6-pamb)/0.5rho), to determine rho : Ps=Pamb, Ts/T6=(Pamb/P6)^(0.4/1.4) 65

66 Low BPR turbofan/jet pre-design Specific thrust of this engine, M0.8 no afterburning T/q = 1 / (1+BPR) x Ve_afterburning + BPR / (1+BPR) x Ve_fan V0 T/q = = 573 N/kg Eta_prop = 2 x T x V / [ BPR/(BPR+1) Ve_fan² + 1/(BPR+1) VE_nozzle² -V0² ] Eta_prop = 2 x T x 0.8 x 340 / [ 0.5 x 1119² x 571² - 272² ] ~ 44% M0.8 Station Pt (Pa) Tt (K) Ambiant Pamb Fan inlet P1/T Fan outlet P2/ Nozzle Ve (m/s) = 571 Station Pt (Pa) Tt (K) GG inlet P2/T Combustion in Combustion o HP Turbine ou LP turbine out Cold nozzle Ve (m/s) = 1119 T/q (kn/kg) Etaprop cold % 66

67 Low BPR turbofan/jet reaching M1.2 Aircraft has accelerated at M1.2, what is the impact on engine thrust > RAM recovery enables higher Fan outlet pressure => more fan thrust > But higher ERAM x FAN x CHP pressure ratio implies higher T3 Enables less fuel burning for equivalent turbine temperature => Core nozzle thrust decreases > Needs to be compensated by afterburning M0.8 M1.2 Station Pt (Pa) Tt (K) Pt (Pa) Tt (K) Ambiant Pamb/Tamb Fan inlet P1/T Fan outlet P2/T Nozzle Ve (m/s) = 571 Ve (m/s) = 718 Station Pt (Pa) Tt (K) Pt (Pa) Tt (K) GG inlet P2/T Combustion inlet P3/T Combustion outlet P4/T HP Turbine outlet T5/P LP turbine outlet T6/P Cold nozzle Ve (m/s) = 1119 Ve (m/s) = K afterburning Ve (m/s) = 1272 T/q (kn/kg) Etaprop 44% 58% 47% cold 573 cold 513 afterburned

68 Low BPR turbofan/jet cruising M0.8 At M0.8, V0² is only 45% of M1.2 > Required thrust at cruise to compensate drag should be 45% lower > To lower engine thrust, fuel burned quantity is decreased => lower turbine inlet temperature As q decreases with turbine temperature, the T/q goal is higher than 45% M1.2 T/q Let s assume a 45% = 67% of M1.2 T/q => T/q = 393 kn/kg > Turbine temperature is only 1540K Component critical design is clearly done by the M1.2 requirement > As nozzle thrust was significantly reduced, propulsion efficiency is increased (from 44% to 57%) Nota : we have considered constant OPR ; however, the compressor speed will decrease with turbine inlet temperature, and so will do the OPR M1.2 M0.8 Station Pt (Pa) Tt (K) Pt (Pa) Tt (K) Ambiant Pamb/Tamb Fan inlet P1/T Fan outlet P2/T Nozzle Ve (m/s) = 718 Ve (m/s) = 571 Station Pt (Pa) Tt (K) Pt (Pa) Tt (K) GG inlet P2/T Combustion inlet P3/T Combustion outlet P4/T HP Turbine outlet T5/P LP turbine outlet T6/P Cold nozzle Ve (m/s) = 1124 Ve (m/s) = K afterburning Ve (m/s) = 1272 T/q (kn/kg) Etaprop 58% 57% 47% cold 513 cold 393 afterburned

69 The ramjet The ram jet is a single combustion right before the jet nozzle Compression is needed to make the combustion efficient enough for propulsion > Use RAM effect to increase pressure in the engine > At inlet Pt = P0 + ½ r V0² => additionnal pressure is proportionnal to square aircraft speed RAMjet can only work with high V0 > Mainly used for rockets launched from the supersonic aircraft > Or associated with one other engine Speed can be initiated by solid propulsion Or can be used hybrid RAM/turbo jets 69

70 Engine as breaking The engine can be used as the main break when landing > Negative staggering of the propeller > Thrust reverser for the turbofan 70